Testosterone is the primary male sex hormone and an anabolic steroid. In men, testosterone plays a key role in the development of male reproductive tissues such as the testis and prostate, and promotes secondary sexual characteristics such as increased muscle and bone mass, and the growth of body hair. Testosterone enanthate is the heptanoic acid derived ester of testosterone, and thus a prodrug of testosterone. Testosterone enanthate is less polar than free testosterone, and affords a sustained in vivo delivery of testosterone upon parenteral administration, by being slowly absorbed from the lipid phase. Thus testosterone enanthate can be administered at longer time intervals, for example one to four weeks.